To expand on my question.I need to replace a 5 band 100k resistor and possibly others but the resistors that I have in my stock of parts for replacements are physically larger than the ones on the current PCB project. Can I use these as replacements? How does the physical size of resistors factor in, or does the size even factor into these components? Further details to describe resistor.The main body colour of both resistors are blue.
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1\$\begingroup\$ Resistor size typically only effects how much power it is capable of dissipating without destructive failure (i.e. burning out). So long as the replacement resistor has the same resistance value, and is the same wattage or higher, you are fine. Usually, larger resistors have a higher power rating, so you should be fine. \$\endgroup\$– ambitiose_sed_ineptumNov 16, 2016 at 21:51
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\$\begingroup\$ When physically larger than the PCB space, consider mounting on end in a standing position vs. flat on the board. \$\endgroup\$– OptionpartyNov 16, 2016 at 21:59
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\$\begingroup\$ Why do you have to replace a 100 kohm resistor - even a quarter watt one needs substantially more than 150 volts to burn it - are you technically equipped for this task given that you appear not to be? It could be lethal voltages? \$\endgroup\$– Andy akaNov 16, 2016 at 22:26
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\$\begingroup\$ @ My soldering skills and troubleshooting skills are just fine. The device is a Jyetech oscilloscope. I got a wrong value or it tested bad.Now I believe that the physical size is attributed to wattage and I am unsure about this detail and I am unsure if you can use larger wattage resistor in place of a lower wattage resistor.Now if this is correct than common sense says that you can't put a smaller one in replacement of a larger one. \$\endgroup\$– KoolBreezeNov 24, 2016 at 19:36
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2 Answers
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For DC and even up to high-frequency AC, the issues are typically only mechanical, not electrical.
However, for very high-frequency AC (VHF or UHF radio frequencies), there may be other factors to consider like bulk capacitance and lead inductance, etc.
So this question/answer doesn't hold up across the entire spectrum. Since we don't know the nature of the circuit, be aware that this is not a 100% universal answer.
answered Nov 16, 2016 at 22:23
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\$\begingroup\$ Mechanical? The question is an easy one how does the physical size of resistors play into electronic circuits. I believe since I asked this question that I discovered that the size equates to their wattage so the questions I have now are is this true and can you put a 5 stripe 100k 1-watt resistor as a replacement for anything lower? \$\endgroup\$ Nov 24, 2016 at 19:40
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Size is not that important (when the replacement part is bigger) but it's a 5-band resistor so make sure that you have a resistor of equivalent tolerance (probably +/-1%) or better and temperature coefficient.
If you replace a precision resistor with, say, a carbon film or composition type the stability of the circuit over temperature and time will likely be greatly compromised.
Resistors are so cheap you might as well just order the correct thing. If it's a 1% resistor replace it with a 1% or better part of the same value and size, and 50ppm/°C or 100ppm/°C. For example, a Stackpole RNMF14FTC100K is about 10-12 cents in single quantity.
answered Nov 16, 2016 at 22:33
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\$\begingroup\$ So it's true that the physical size equates to their wattage? This would allow you to use a higher wattage as replacements? The device is a Jyetech oscilloscope one or more of the resistors are either wrong or bad and I just need to be able to have it start so I know if it will work or not, for example, there is a resistor that needs a 2 mil and the one I have only has a 1.8 mil so I was thinking if I joined 2 1mil in parallel this would at least let me start it but the size of resistors has always thrown me off until now if my hypothesis about size to wattage is correct. \$\endgroup\$ Nov 24, 2016 at 19:41
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\$\begingroup\$ It's correlated but sometimes smaller parts are made to run hotter. That's rare with 5-band resistors where precision counts. Using a higher wattage rated part is always okay if the other characteristics are the same or better. Don't replace a 0.25W precision resistor with a 1W non-precision type, in other words. \$\endgroup\$ Nov 24, 2016 at 19:44